The present invention relates to a leukocyte-removing filter medium for removing leukocytes from a leukocyte-containing fluid such as a whole blood product or a red cell concentrate, and a method for removing leukocytes by the use of the leukocyte-removing filter medium.
In the field of blood transfusion, in addition to so-called whole blood transfusion comprising transfusing a whole blood product obtained by adding an anticoagulant to blood collected from a blood donor, so-called component transfusion comprising separating a blood component necessary to a blood recipient from the whole blood product and transfusing the blood component is generally carried out. The component transfusion is classified into red cell transfusion, platelet transfusion, plasma transfusion, etc. according to the species of blood component necessary to a blood recipient. Blood component products used in these blood transfusions include red cell products, platelet products, plasma products, etc. In recent years, a so-called leukocyte-free blood transfusion has been commonly used in which a blood product is transfused after being freed of leukocytes contained therein as contaminants. This is because it has been revealed that relatively slight side effects accompanying blood transfusion, such as headache, nausea, chill, non-hemolytic pyretic reaction, etc., and serious side effects such as alloantigen sensitization, viral infection, post transfusion GVHD, etc., which have serious influences on a blood recipient, are caused mainly by leukocytes contained as contaminants in a blood product used in transfusion.
It is said that to prevent the relatively slight side effects such as headache, nausea, chill, pyrexia, etc., it is sufficient that leukocytes in a blood product are removed until their residual ratio becomes less than 10xe2x88x921-10xe2x88x922. It is also said that to prevent the serious side effects such as alloantigen sensitization, viral infection, etc., it is sufficient that leukocytes are removed until their residual ratio becomes less than 10xe2x88x924-10xe2x88x926.
Methods for removing leukocytes from a blood product are divided broadly into two categories, i.e., centrifugation methods in which leukocytes are separated and removed with a centrifuge by utilizing the difference in specific gravity among blood components, and filter methods in which leukocytes are removed by using a filter medium composed of a fibrous material or a porous element such as a porous material having intercommunicating voids. The filter methods have been commonly used at present because they have advantages such as excellent leukocyte-removing capability, easy operations, and low cost. Of the filter methods, a method of removing leukocytes by adhesion or adsorption using, as a filter medium, a nonwoven fabric or a porous material having intercommunicating voids, is the most widespread at present because of its especially excellent leukocyte-removing capability.
As to the mechanism of the removal of leukocytes by the use of the above-mentioned filter medium composed of a fibrous material or a porous material, it is considered that the removal is caused mainly because leukocytes brought into contact with the filter medium surface are adhered to or adsorbed on the filter medium surface. Therefore, increasing the frequency of collision between the filter medium and leukocytes, i.e., reducing the fiber diameter or the pore size of the filter medium or increasing the packing density of the filter medium in an filter apparatus, has been investigated as a means for improving the leukocyte-removing capability of conventional filter media. However, there has been a limit in the improvement of the leukocyte-removing capability by the use of only the above means in the case of a product having a high red cell content, such as a whole blood product or a red cell product. That is, the frequency of contact of red cells, containted at a high concentration in the product, with the filter medium and the resistance to fluid passage increase, with an increase of the frequency of contact of leukocytes with the filter medium. Thus, there have been problems such as the prolonged treatment time and hemolysis due to the breakage of red cell membrane.
On the other hand, investigations have been conducted based on the knowledge of surface chemical properties of filter media. JP-A-1/249063 discloses a filter medium having a hydrophilic and negatively charged surface. WO 87/05812 discloses a filter medium containing nonionic hydrophilic groups and basic nitrogen-containing functional groups and having a content of the basic nitrogen-containing functional groups of less than 4.0% by weight and not less than 0.2% by weight. These techniques, however, are intended for maintaining the leukocyte-removing capability while improving the passage rate of platelets known as very adhesive cells, and hardly make further improvement in the leukocyte-removing capability. The technique disclosed in EP 0500472-A2 is not intended for increasing the removal rate of leukocytes but for increasing the removal rate of platelets while maintaining a satisfactory capability of passing red cells, by using a filter medium with a positive zeta potential in the removal of leukocytes and platelets from a red cell product. JP-A-6/24782 discloses a filter medium which contains basic functional groups and nonionic hydrophilic groups, has a molar ratio of the basic functional groups to the nonionic hydrophilic groups of less than 6 and not less than 0.6, and contains the basic functional groups at a density of less than 0.1 meq/m2 and not less than 5xc3x9710xe2x88x925 meq/m2. This filter medium, however, does not have sufficient inhibitory effect on the adhesion of red cells and hardly makes stable improvement in the leukocyte-removing capability.
A first object of the present invention is to provide a filter medium which suppresses the adhesion of red cells thereto, has a very high affinity for leukocytes, has an especially high leukocyte-removing capability, permits a satisfactory flow of a leukocyte-containing fluid, and has an excellent blood compatibility. This filter medium has, at least on its surface, hydrophilic basic groups containing at least one nonionic hydrophilic portion and at least one basic portion, in which said hydrophilic portion(s) is located nearer to the end of the hydrophilic basic group than said basic portion(s) is. The present inventors found that the above first object can be achieved by using such a leukocyte-removing filter medium.
That is, the present invention relates to a leukocyte-removing filter medium for removing leukocytes from a leukocyte-containing fluid, wherein the filter medium has, at least on its surface, hydrophilic basic groups containing at least one nonionic hydrophilic portion and at least one basic portion, in which the hydrophilic portion(s) is located nearer to the end of the hydrophilic basic group than said basic portion(s) is.
A second object of the present invention is to provide a method for removing leukocytes with a very high efficiency from a leukocyte-containing fluid such as a whole blood product, a red cell concentrate or the like while suppressing the adhesion of red cells. The present inventors found that the above second object can be achieved by using an apparatus comprising at least an inlet, a filter comprising the leukocyte-removing filter medium of the present invention properly located therein, and an outlet, thereby introducing a leukocyte-containing fluid through the inlet, and recovering through the outlet the fluid filtered through the filter.
That is, the present invention relates to a method for removing leukocytes from a leukocyte-containing fluid, which comprises using an apparatus comprising at least 1) an inlet, 2) a filter comprising the leukocyte-removing filter medium of claim 1 and 3) an outlet, wherein the method comprises introducing the leukocyte-containing fluid through the inlet, and recovering through the outlet the fluid filtered through said filter.